iOS/Android: Facebook continued its tradition of breaking out functionality into separate apps with Groups today. The app will make it easier to create, manage, and interact with private groups on the service.
Much like many other Facebook features, Groups has been integrated into the main Facebook app for a while now, but it doesn't get the love it probably deserves as a feature of a larger app. The new app comes with a slick new interface and can presumably be updated without worrying about what the main Facebook app is doing.
If you don't use Groups that often and don't want to install yet another app, don't worry. Facebook isn't making this one mandatory. The app is rolling out now for iOS and Android, though if you're not seeing it on your device, just give it a bit. The rollout should be completed today.
Facebook Groups | Google Play Store
Facebook Groups | iTunes App Store